1. Field of the Invention
The present invention relates to a tire pressure control device that regulates the tire pressure for a vehicle, a tire pressure control system that includes the tire pressure control device, and a tire pressure control method.
2. Background of the Invention
A conventional apparatus that supplies air pressure from a vehicle body side to a tire when a tire pressure is determined to be decreasing based on the information obtained by using a control device provided in the vehicle body and a tire pressure sensor installed on the wheel side to detect the tire pressure (see, e.g., Japanese Patent Application Publication No. JP-A-2003-326928).
A compressor that compresses air, a reservoir that retains the compressed air, and an electronic valve that regulates the air pressure supplied to and discharged from a tire, are provided on the vehicle body side. At least a tire pressure sensor is provided on the wheel side. In addition, a seal member to ensure an airtight seal is provided at a portion where a line from the wheel is connected with a line from the vehicle body. A signal detected by the tire pressure sensor in each of the wheels is transmitted to the control device in the vehicle body side via a communication line.
Recently, a tire pressure monitoring system (hereinafter, referred to as “TPMS”) has also been provided. The TPMS includes a wheel side device for detecting the tire pressure at each wheel and transmitting the tire pressure information by wireless transmission; and a vehicle body side apparatus that receives the transmitted tire pressure information and monitors the tire pressure at each wheel. In the TPMS, a transmitter that transmits wheel information, including the tire pressure information, is provided at each wheel and an electronic control unit (hereinafter, referred to as “ECU”) that receives the wheel information to perform specified operation processes thereon, and displaying the information indicating tire pressure deficiency and the like on an indicator is provided at the vehicle body side.
Thus, in a vehicle equipped with the TMPS, it is considered to be efficient to control the tire pressure based on the tire pressure information received through the wireless transmission from the wheel side device. However, in case that the vehicle body side cannot receive the tire pressure information, it becomes difficult to supply the air pressure to the tire.
At first, Radio Regulation Laws in different countries need to be considered. For example, since North America and Japan have different Radio Regulation Laws, an output level of radio waves permitted in North America may not be permitted in Japan. In that case, when a vehicle equipped with the TPMS fitted to be used in North America receives a transmission stop instruction through a specified tool in a vehicle assembly factory in Japan, the transmission from the transmitter is temporarily stopped. At this time, the transmitter of each wheel transmits a sleep signal indicating that there will be no further transmission after transmitting thereof to the vehicle body apparatus and transfers the driving mode of the vehicle to a transmission stop mode. When receiving the sleep signal, the ECU makes an indicator lamp blink several times in order to notify that transmission is stopped, but also continues to perform other processing thereafter, without determining a state that there are no received radio waves from the transmitter as an anomaly. As a result, even if the tire pressure decreases during the transmission stop mode of the transmitter, the ECU does not regulate the tire pressure and, also, a driver cannot recognize the tire pressure decrease. The anomaly in the tire pressure will be detected for the first time when being driven again by using a specified tool after the vehicle is exported to and arrives in North America.
Next, there may be various noises in the environment, and, accordingly, a noise having a similar pattern with that of the transmission stop instruction from the aforementioned tool may be included therein. When receiving such a noise, the transmitter may confuse the noise with the transmission stop instruction to stop the transmission. As a result, even if the tire pressure decreases, the ECU cannot recognize the tire pressure decrease. In case that the vehicle side apparatus cannot normally receive transmission waves from the transmitter, e.g., due to other noises or interfering waves generated in the environment, the ECU cannot process the tire pressure information.
In addition, when the TPMS itself has been broken down, the vehicle body cannot normally receive the tire pressure information thereafter, and therefore the ECU does not recognize the tire pressure decrease even if the tire pressure actually decreases. In such a case of the TPMS breaking down as aforementioned, the indicator lamp is turned on to notify the breakdown of the TPMS, but a driver may not understand why the indicator lamp is turned on. In that case, it is probable that the driver drives the vehicle even while the TPMS does not work and the driver feels a change in a tire state until the vehicle is brought into a dealer.
The above-described problems are caused in the TPMS in which information is wirelessly transmitted. However, similar problems may be caused even in a TPMS that indirectly estimates the tire pressure using a wheel speed sensor. These problems may be caused when an ECU becomes unable to process the tire pressure information due to a malfunction in the wheel speed sensor or braking of a wire from the wheel speed sensor to the ECU.
Meanwhile, there may be considered a system configured such that an tire pressure regulating device is constantly operated regardless of whether the tire pressure decreases, and when the tire pressure exceeds a specified value, the excess air is discharged to the outside by using a pressure regulating valve. However, this system is inefficient in that the tire pressure regulating device is unnecessarily driven and has trouble with durability such that the seal member for ensuring airtightness is prone to wear by sliding friction.